/*
 * Copyright 2015-present Open Networking Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.onosproject.store.service;

import java.util.Collection;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.Executor;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;

import com.google.common.util.concurrent.MoreExecutors;
import org.onosproject.store.primitives.DefaultConsistentMap;
import org.onosproject.store.primitives.MapUpdate;

/**
 * A distributed, strongly consistent map whose methods are all executed asynchronously.
 * <p>
 * This map offers strong read-after-update (where update == create/update/delete)
 * consistency. All operations to the map are serialized and applied in a consistent
 * manner.
 * <p>
 * The stronger consistency comes at the expense of availability in
 * the event of a network partition. A network partition can be either due to
 * a temporary disruption in network connectivity between participating nodes
 * or due to a node being temporarily down.
 * </p><p>
 * All values stored in this map are {@link Versioned versioned} and the API
 * supports optimistic concurrency by allowing conditional updates that take into
 * consideration the version or value that was previously read.
 * </p><p>
 * This map does not allow null values. All methods can throw a ConsistentMapException
 * (which extends {@code RuntimeException}) to indicate failures.
 * <p>
 * All methods of this interface return a {@link CompletableFuture future} immediately
 * after a successful invocation. The operation itself is executed asynchronous and
 * the returned future will be {@link CompletableFuture#complete completed} when the
 * operation finishes.
 */
public interface AsyncConsistentMap<K, V>
    extends DistributedPrimitive, Transactional<MapUpdate<K, V>>, AsyncIterable<Map.Entry<K, Versioned<V>>> {

    @Override
    default DistributedPrimitive.Type primitiveType() {
        return DistributedPrimitive.Type.CONSISTENT_MAP;
    }

    @Override
    default CompletableFuture<Void> destroy() {
        return clear();
    }

    /**
     * Returns the number of entries in the map.
     *
     * @return a future for map size.
     */
    CompletableFuture<Integer> size();

    /**
     * Returns true if the map is empty.
     *
     * @return a future whose value will be true if map has no entries, false otherwise.
     */
    default CompletableFuture<Boolean> isEmpty() {
        return size().thenApply(s -> s == 0);
    }

    /**
     * Returns true if this map contains a mapping for the specified key.
     *
     * @param key key
     * @return a future whose value will be true if map contains key, false otherwise.
     */
    CompletableFuture<Boolean> containsKey(K key);

    /**
     * Returns true if this map contains the specified value.
     *
     * @param value value
     * @return a future whose value will be true if map contains value, false otherwise.
     */
    CompletableFuture<Boolean> containsValue(V value);

    /**
     * Returns the value (and version) to which the specified key is mapped, or null if this
     * map contains no mapping for the key.
     *
     * @param key the key whose associated value (and version) is to be returned
     * @return a future value (and version) to which the specified key is mapped, or null if
     * this map contains no mapping for the key
     */
    CompletableFuture<Versioned<V>> get(K key);

    /**
     * Returns the value (and version) to which the specified key is mapped, or the provided
     * default value if this map contains no mapping for the key.
     *
     * @param key the key whose associated value (and version) is to be returned
     * @param defaultValue the default value to return if the key is not set
     * @return a future value (and version) to which the specified key is mapped, or null if
     * this map contains no mapping for the key
     */
    CompletableFuture<Versioned<V>> getOrDefault(K key, V defaultValue);

    /**
     * If the specified key is not already associated with a value (or is mapped to null),
     * attempts to compute its value using the given mapping function and enters it into
     * this map unless null.
     * If a conflicting concurrent modification attempt is detected, the returned future
     * will be completed exceptionally with ConsistentMapException.ConcurrentModification.
     * @param key key with which the specified value is to be associated
     * @param mappingFunction the function to compute a value
     * @return the current (existing or computed) value associated with the specified key,
     * or null if the computed value is null
     */
    default CompletableFuture<Versioned<V>> computeIfAbsent(K key,
            Function<? super K, ? extends V> mappingFunction) {
        return computeIf(key, Objects::isNull, (k, v) -> mappingFunction.apply(k));
    }

    /**
     * If the value for the specified key is present and non-null, attempts to compute a new
     * mapping given the key and its current mapped value.
     * If the computed value is null, the current mapping will be removed from the map.
     * If a conflicting concurrent modification attempt is detected, the returned future
     * will be completed exceptionally with ConsistentMapException.ConcurrentModification.
     * @param key key with which the specified value is to be associated
     * @param remappingFunction the function to compute a value
     * @return the new value associated with the specified key, or null if computed value is null
     */
    default CompletableFuture<Versioned<V>> computeIfPresent(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        return computeIf(key, Objects::nonNull, remappingFunction);
    }

    /**
     * Attempts to compute a mapping for the specified key and its current mapped value (or
     * null if there is no current mapping).
     * If the computed value is null, the current mapping (if one exists) will be removed from the map.
     * If a conflicting concurrent modification attempt is detected, the returned future
     * will be completed exceptionally with ConsistentMapException.ConcurrentModification.
     * @param key key with which the specified value is to be associated
     * @param remappingFunction the function to compute a value
     * @return the new value associated with the specified key, or null if computed value is null
     */
    default CompletableFuture<Versioned<V>> compute(K key,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        return computeIf(key, v -> true, remappingFunction);
    }

    /**
     * If the value for the specified key satisfies a condition, attempts to compute a new
     * mapping given the key and its current mapped value.
     * If the computed value is null, the current mapping will be removed from the map.
     * If a conflicting concurrent modification attempt is detected, the returned future
     * will be completed exceptionally with ConsistentMapException.ConcurrentModification.
     * @param key key with which the specified value is to be associated
     * @param condition condition that should evaluate to true for the computation to proceed
     * @param remappingFunction the function to compute a value
     * @return the new value associated with the specified key, or the old value if condition evaluates to false
     */
    CompletableFuture<Versioned<V>> computeIf(K key,
            Predicate<? super V> condition,
            BiFunction<? super K, ? super V, ? extends V> remappingFunction);

    /**
     * Associates the specified value with the specified key in this map (optional operation).
     * If the map previously contained a mapping for the key, the old value is replaced by the
     * specified value.
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return the previous value (and version) associated with key, or null if there was
     * no mapping for key.
     */
    CompletableFuture<Versioned<V>> put(K key, V value);

    /**
     * Associates the specified value with the specified key in this map (optional operation).
     * If the map previously contained a mapping for the key, the old value is replaced by the
     * specified value.
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return new value.
     */
    CompletableFuture<Versioned<V>> putAndGet(K key, V value);

    /**
     * Removes the mapping for a key from this map if it is present (optional operation).
     *
     * @param key key whose value is to be removed from the map
     * @return the value (and version) to which this map previously associated the key,
     * or null if the map contained no mapping for the key.
     */
    CompletableFuture<Versioned<V>> remove(K key);

    /**
     * Removes all of the mappings from this map (optional operation).
     * The map will be empty after this call returns.
     * @return future that will be successfully completed when the map is cleared
     */
    CompletableFuture<Void> clear();

    /**
     * Returns a Set view of the keys contained in this map.
     * This method differs from the behavior of java.util.Map.keySet() in that
     * what is returned is a unmodifiable snapshot view of the keys in the ConsistentMap.
     * Attempts to modify the returned set, whether direct or via its iterator,
     * result in an UnsupportedOperationException.
     *
     * @return a set of the keys contained in this map
     */
    CompletableFuture<Set<K>> keySet();

    /**
     * Returns the collection of values (and associated versions) contained in this map.
     * This method differs from the behavior of java.util.Map.values() in that
     * what is returned is a unmodifiable snapshot view of the values in the ConsistentMap.
     * Attempts to modify the returned collection, whether direct or via its iterator,
     * result in an UnsupportedOperationException.
     *
     * @return a collection of the values (and associated versions) contained in this map
     */
    CompletableFuture<Collection<Versioned<V>>> values();

    /**
     * Returns the set of entries contained in this map.
     * This method differs from the behavior of java.util.Map.entrySet() in that
     * what is returned is a unmodifiable snapshot view of the entries in the ConsistentMap.
     * Attempts to modify the returned set, whether direct or via its iterator,
     * result in an UnsupportedOperationException.
     *
     * @return set of entries contained in this map.
     */
    CompletableFuture<Set<Entry<K, Versioned<V>>>> entrySet();

    /**
     * If the specified key is not already associated with a value associates
     * it with the given value and returns null, else behaves as a get
     * returning the existing mapping without making any changes.
     *
     * @param key key with which the specified value is to be associated
     * @param value value to be associated with the specified key
     * @return the previous value associated with the specified key or null
     * if key does not already mapped to a value.
     */
    CompletableFuture<Versioned<V>> putIfAbsent(K key, V value);

    /**
     * Removes the entry for the specified key only if it is currently
     * mapped to the specified value.
     *
     * @param key key with which the specified value is associated
     * @param value value expected to be associated with the specified key
     * @return true if the value was removed
     */
    CompletableFuture<Boolean> remove(K key, V value);

    /**
     * Removes the entry for the specified key only if its current
     * version in the map is equal to the specified version.
     *
     * @param key key with which the specified version is associated
     * @param version version expected to be associated with the specified key
     * @return true if the value was removed
     */
    CompletableFuture<Boolean> remove(K key, long version);

    /**
     * Replaces the entry for the specified key only if there is any value
     * which associated with specified key.
     *
     * @param key key with which the specified value is associated
     * @param value value expected to be associated with the specified key
     * @return the previous value associated with the specified key or null
     */
    CompletableFuture<Versioned<V>> replace(K key, V value);

    /**
     * Replaces the entry for the specified key only if currently mapped
     * to the specified value.
     *
     * @param key key with which the specified value is associated
     * @param oldValue value expected to be associated with the specified key
     * @param newValue value to be associated with the specified key
     * @return true if the value was replaced
     */
    CompletableFuture<Boolean> replace(K key, V oldValue, V newValue);

    /**
     * Replaces the entry for the specified key only if it is currently mapped to the
     * specified version.
     *
     * @param key key key with which the specified value is associated
     * @param oldVersion version expected to be associated with the specified key
     * @param newValue value to be associated with the specified key
     * @return true if the value was replaced
     */
    CompletableFuture<Boolean> replace(K key, long oldVersion, V newValue);

    /**
     * Registers the specified listener to be notified whenever the map is updated.
     *
     * @param listener listener to notify about map events
     * @return future that will be completed when the operation finishes
     */
    default CompletableFuture<Void> addListener(MapEventListener<K, V> listener) {
        return addListener(listener, MoreExecutors.directExecutor());
    }

    /**
     * Registers the specified listener to be notified whenever the map is updated.
     *
     * @param listener listener to notify about map events
     * @param executor executor to use for handling incoming map events
     * @return future that will be completed when the operation finishes
     */
    CompletableFuture<Void> addListener(MapEventListener<K, V> listener, Executor executor);

    /**
     * Unregisters the specified listener such that it will no longer
     * receive map change notifications.
     *
     * @param listener listener to unregister
     * @return future that will be completed when the operation finishes
     */
    CompletableFuture<Void> removeListener(MapEventListener<K, V> listener);

    /**
     * Returns a new {@link ConsistentMap} that is backed by this instance.
     *
     * @return new {@code ConsistentMap} instance
     */
    default ConsistentMap<K, V> asConsistentMap() {
        return asConsistentMap(DistributedPrimitive.DEFAULT_OPERATION_TIMEOUT_MILLIS);
    }

    /**
     * Returns a new {@link ConsistentMap} that is backed by this instance.
     *
     * @param timeoutMillis timeout duration for the returned ConsistentMap operations
     * @return new {@code ConsistentMap} instance
     */
    default ConsistentMap<K, V> asConsistentMap(long timeoutMillis) {
        return new DefaultConsistentMap<>(this, timeoutMillis);
    }
}
